Most research to date using animal models of drug abuse has focused on the effects of psychostimulants on brain neurochemistry and behavior in adult, prenatal, or preweanling animals. There has been little research focusing on the effects of psychostimulants on adolescent rats even though it is well known that a large number of people who use drugs started as teenagers. Because of this, it is of interest to examine the effects of psychostimulants in the adolescent population in order to determine whether there may be a difference in how this class of drugs effects this age cohort. Sex differences in periadolescent and adult rats may be important in determining the behavioral and neurochemical effects of psychostimulants and this should be taken into account when researching the effects of these drugs. Therefore, the effects of cocaine and methylphenidate on behavior and neurochemistry in female periadolescent and adult rats will be examined in this study. An understanding of the differential effects of drugs during periadolescence and adulthood in females may lead to different treatments for males and females in different age groups.